In the processing of webs of paper, plastics, textile fabrics and the like, a liquid or sticky component or coating of a web may render support thereof during its advancement impractical by any means except a gaseous medium. Examples of an apparatus utilizing a gaseous medium for "floating" such webs are disclosed in U.S. Pat. Nos. 3,837,551; 3,549,070; 3,452,447; and others. In general, the web is supported within an oven or chamber until it has reached a physical state in its linear advancement in which it can be brought into contact with other materials or supporting media. Commercially important parameters of gaseous web suspension are the length of the chamber in which web floating is effected and the processing rate or web travel. For example, chamber lengths of not greater than about 30 feet may be used for economic or space reasons. Some web machinery is paced at linear rates as high as 2000 feet per minute or more. While the apparatus of U.S. Pat. No. 3,837,551 is especially designed, and perhaps superior, for handling the lighter weight webs heretofore encountered in web-treating technology and is notable for achievement of the highest heat transfer rates in the industry, there remains the tendency (1) to cause streaking in some web coatings resulting, it is believed, from the lateral migration of a component in the coating composition, and in other cases, the physical deformation of the coating, and (2) corrugations extending lengthwise of the very weak webs apparently resulting from deformation of the web by impingement of jets thereon issuing from the openings in the pads. Any alteration in pad design tending to alleviate these disadvantages tends to reduce the heat transfer coefficient on transferring heat from the gaseous suspending medium to the web. If the heat transfer coefficient is reduced, the length of the web treating chamber must be extended and/or the rate of web movement reduced.
It is an essential object of the invention to provide equipment for subjecting very weak or thin webs to drying or heat-treating operations by a gaseous medium which are too difficult to satisfactorily process by known apparatus.
Another object is to accomplish the foregoing objects with equipment that affects high heat transfer values between the gaseous medium and the web.
A further object is to devise equipment that will dispense a gaseous medium in a manner which avoids damaging variations in velocity and pressure as measured transversely of the web in the contact of the gaseous medium with the web.
Another object is to provide the equipment of the foregoing objects in a form inexpensively fashioned from sheet material, such as sheet metal shapes, stamping, and the like.